This invention relates to the field of dial indicators, and in particular to a low mass needle used for a pressure indicating mechanism.
Pressure measuring devices, such as for sphygmomanometers used for measuring blood pressure, include a pneumatic bulb which inflates a pressure chamber of an attached sleeve that is fitted over the arm or leg of patient. A diaphragm or bellows assembly, responsive to changes in fluid pressure of the pneumatic bulb and the sleeve pressure chamber, is positioned in a dial indicator housing. The pointer of a dial indicator is interconnected to a bellows assembly by a movement mechanism, whereby inflation of the bellows causes corresponding circumferential movement of the pointer.
Traditionally, brass, steel, or aluminum have been the preferred materials for pointers of the above-type devices. Conventional pointer elements, however, exhibit an undesirable level of instability during use, borne from the mass of the pointer, which creates a stress load on the measuring mechanism, and degrades the overall accuracy and responsiveness of the device. For example, a conventional brass pointer is approximately 0.008 inches thick. A plastic pointer having an equivalent stiffness would therefore have to be approximately three times as thick as the brass pointer design, ordinarily negating a low mass design. As a result of the above load and instability, frequent calibration is also required to properly null the device which leads to a reduction in the useful life of the mechanism.
Consequently, there are preexisting needs in the field to provide a low mass pointer element for use in a pressure measuring mechanism which can be manufactured and assembled with reduced costs than those which are previously known.
It is a primary object of the present invention to improve the state of the art of dial indicators.
It is a further primary object to be able to improve the useful life of a dial pressure or other indicator mechanism.
It is yet another primary object of the present invention to improve the repeatability of a pressure indicating mechanism.
Therefore and according to a preferred aspect of the present invention, there is provided in a pressure measuring mechanism having a dial face gauge, a low mass pointer element comprising:
a center hub capable of being fitted onto an extending axial shaft of said measuring mechanism, the center hub having a recess for receiving a locking member of said axial shaft, an indicator portion extending from said center hub, and a counterbalance portion. The counterbalance portion oppositely extends from the center hub, in which the indicator portion being inwardly tapered to a blade-like end and in which said pointer element is formed form a lightweight material.
The center hub of the pointer element can also include a through aperture for receiving a protruding end of the axial shaft with the locking member extending integrally as well from the shaft end.
According to another preferred aspect of the present invention, there is provided a movement mechanism comprising an axial shaft member having opposing first and second ends, axial displacement means for moving the first end of said shaft member in an axial direction, and at least one spring member coaxially positioned relative to said shaft member axis. The spring member is attached at one end to an intermediate portion of said shaft member and attached at an opposite end to a support, wherein the displacement means causes said shaft member to translate in said axial direction, said spring member to flex, and said shaft member to rotate. The movement mechanism further includes a dial face having measuring indicia fitted around the first end of said axial shaft member and a low mass pointer element fitted onto the first end of said axial shaft member, the low mass pointer element capable of circumferential movement relative to the dial face.
A distinct advantage of the present invention is that by making a plastic pointer with a tapered triangular configuration as preferably described equivalent stiffness to that of a metal pointer can be realized, but with significant mass reductions creating a considerable reduction in load to the movement mechanism while actually improving overall performance.
An advantage of the present invention is that a low mass needle as described herein has a significantly lower mass than any others previously known in the field due largely to the tapered cross section which adds significantly to the overall fatigue life of the gauge and measuring mechanism used in conjunction with the pointer.
Yet another advantage of the present invention is that the described pointer element can be repeatably aligned with the axial shaft member of the movement mechanism, thereby aiding in the manufacture and the calibration of a measuring device.